U.S. patent application number 15/846898 was filed with the patent office on 2018-04-19 for heat exchangers for low temperature carbon dioxide separation from natural gas.
The applicant listed for this patent is UOP LLC. Invention is credited to Thomas J. Godry, Zhanping Xu, Lubo Zhou.
Application Number | 20180106535 15/846898 |
Document ID | / |
Family ID | 57608663 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180106535 |
Kind Code |
A1 |
Zhou; Lubo ; et al. |
April 19, 2018 |
HEAT EXCHANGERS FOR LOW TEMPERATURE CARBON DIOXIDE SEPARATION FROM
NATURAL GAS
Abstract
A reboiler in fluid communication with a fractionator column in
an offshore low temperature process removing carbon dioxide from
natural gas has a vessel volume. A carbon steel tubing bundle is
disposed within the vessel volume. Each tube in the bundle has an
outer surface with a porous granular metal layer deposited thereon.
The granular metal layer comprises a pore size distribution which
promotes bubble nucleation during vaporization of a nearly pure
liquid carbon dioxide stream.
Inventors: |
Zhou; Lubo; (Inverness,
IL) ; Godry; Thomas J.; (Kenmore, NY) ; Xu;
Zhanping; (Inverness, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
57608663 |
Appl. No.: |
15/846898 |
Filed: |
December 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2016/037971 |
Jun 17, 2016 |
|
|
|
15846898 |
|
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62186945 |
Jun 30, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 13/187 20130101;
F28F 1/42 20130101; F28F 21/082 20130101; B01D 53/00 20130101; C10L
2290/541 20130101; F25J 3/0209 20130101; F25J 3/0233 20130101; F25J
5/00 20130101; F25J 2200/72 20130101; F25J 3/0266 20130101; F25J
2200/02 20130101; F28D 1/0213 20130101; F28F 2009/226 20130101;
F28F 1/40 20130101; F25J 2200/50 20130101; F28D 2021/0064 20130101;
Y02P 70/34 20151101; F28F 1/12 20130101; Y02C 10/12 20130101; B01D
3/322 20130101; F25J 2290/72 20130101; F28D 7/06 20130101; F25J
2250/02 20130101; F25J 2290/44 20130101; C10L 3/104 20130101; B01D
2256/245 20130101; B01D 53/002 20130101; Y02P 70/10 20151101; Y02C
20/40 20200801; B01D 1/02 20130101; F25J 5/005 20130101; B01D 1/04
20130101; B01D 2256/22 20130101; F28F 13/10 20130101 |
International
Class: |
F25J 5/00 20060101
F25J005/00; F28F 21/08 20060101 F28F021/08; F28F 13/18 20060101
F28F013/18; F25J 3/02 20060101 F25J003/02 |
Claims
1. A reboiler in fluid communication with a fractionator column in
an offshore low temperature system removing carbon dioxide from
natural gas, the bottom reboiler comprising: a rigid vessel having
an outer shell defining a vessel volume, the rigid vessel having an
inlet in fluid communication with a fractionator for receiving a
liquid stream therefrom and an outlet for returning a vapor to the
fractionator; and a carbon steel tubing bundle disposed within the
vessel volume each tube in the carbon steel tubing bundle having an
outer surface and an inner surface, the outer surface having a
granular metal layer deposited thereon, and the inner surface being
generally smooth relative thereto, wherein the granular metal layer
comprises a pore size distribution adapted to promote and increase
bubble nucleation during vaporization of a nearly pure liquid
carbon dioxide stream on the outer surfaces of the tubes.
2. The reboiler of claim 1 wherein the granular metal layer is
metallurgically bonded to each tube in the carbon steel tubing
bundle.
3. The reboiler of claim 1 wherein the shell is produced from a
carbon steel.
4. The reboiler of claim 1 wherein a weight of the reboiler is less
than 27,000 kg.
5. The reboiler of claim 1 wherein a weight of the reboiler is less
than 22,000 kg.
6. The reboiler of claim 1 wherein the outer surface having the
granular metal layer deposited thereon increases an overall heat
transfer coefficient of each tube in the carbon steel tubing bundle
by at least 1.3 times that of a bare outer surface of a tube in an
otherwise identical carbon steel tubing bundle.
7. The reboiler of claim 1 wherein the inner surface has a
plurality of fins extending radially inwardly relative thereto.
8. The reboiler of claim 1 wherein the reboiler is a bottom
reboiler which receives a liquid bottoms stream from a fractionator
column.
9. The reboiler of claim 1 wherein the carbon steel tubing bundle
is horizontally disposed within the vessel volume.
10. The reboiler of claim 1 wherein the nearly pure liquid carbon
dioxide stream within the reboiler has a purity of greater than 90
mol %.
11. The reboiler of claim 1 wherein the nearly pure liquid carbon
dioxide stream within the reboiler has a purity greater than 95 mol
%.
12. The reboiler of claim 1 wherein the nearly pure liquid carbon
dioxide stream within the reboiler has a purity of about 97 mol
%.
13. The reboiler of claim 1 wherein a temperature of a bottoms
stream entering the reboiler is between 10.4.degree. C. and
10.8.degree. C.
14. The reboiler of claim 1 wherein a bottoms stream inlet
operating pressure is about 46.5 bar-g.
15. The reboiler of claim 1 wherein a tube-side stream temperature
within the carbon steel tubing bundle is between 20.9.degree. C.
and 32.5.degree. C.
16. The reboiler of claim 1 wherein a tube-side stream temperature
within the carbon steel tubing bundle is between 15.5.degree. C.
and 25.0.degree. C.
17. The reboiler of claim 1 wherein an outside tube diameter in the
carbon steel tubing bundle is less than 5.0 cm.
18. The reboiler of claim 1 wherein an outside tube diameter in the
carbon steel tubing bundle is less than or equal to 2.5 cm.
19. A reboiler in fluid communication with a fractionator column in
an offshore low temperature system removing carbon dioxide from
natural gas, the reboiler comprising: a rigid vessel having a
carbon steel outer shell defining a vessel volume, the rigid vessel
having an inlet in fluid communication with the fractionator for
receiving a liquid stream therefrom and an outlet for returning a
vapor to the fractionator; a carbon steel tubing bundle
horizontally disposed within the vessel volume, each tube in the
carbon steel bundle having an outer surface and an inner surface,
the outer surface having a granular metal layer deposited thereon,
and the inner surface having a plurality of fins extending radially
inwardly relative thereto, wherein the granular metal layer
comprises a pore size distribution adapted to promote and increase
a bubble nucleation during vaporization of liquid carbon dioxide on
the outer surfaces of the tubes; and a liquid carbon dioxide stream
within the rigid vessel having a purity greater than 90 mol %,
wherein the outer surface having the granular metal layer deposited
thereon increases an overall heat transfer coefficient (U-value) of
each tube in the carbon steel tubing bundle at least 1.3 times that
of a bare outer surface of a tube in an otherwise identical carbon
steel tubing bundle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of copending
International Application No. PCT/US2016/037971 filed Jun. 17, 2016
which application claims benefit of U.S. Provisional Application
No. 62/186,945 filed Jun. 30, 2015, now expired, the contents of
which cited applications are hereby incorporated by reference in
their entirety.
FIELD OF THE INVENTION
[0002] This invention relates generally to heat exchangers used in
a process for removing carbon dioxide from natural gas, and more
particularly to a reboiler in an offshore low temperature
distillation processes for removing carbon dioxide from natural
gas.
BACKGROUND OF THE INVENTION
[0003] Carbon dioxide removal from natural gas to meet
specifications can in principle be achieved through the use of
different sweetening technologies. Examples of applicable
technology options for carbon dioxide removal are chemical and
physical absorption, membrane separation, pressure-swing adsorption
(PSA), and cryogenic/low-temperature distillation.
[0004] In a known low-temperature distillation process, methane is
withdrawn from the top of a distillation column and carbon dioxide
and heavy hydrocarbons are withdrawn from the bottom. Heat
exchangers are used in the distillation process to cool the feed
stream from gas to liquid phase or reboil liquid in the column to
generate vapor phase for mass transfer between the phases based on
difference in volatilities.
[0005] Recently, it has been proposed that a cryogenic/low
temperature distillation system can be used to remove carbon
dioxide from offshore natural gas fields. These gas fields may
contain as little as 30% hydrocarbons and 70% carbon dioxide. The
offshore system will have to reduce the carbon dioxide level
dramatically to produce a usable product. Such offshore processing
systems face significant difficulties due to the offshore
environment.
[0006] For example, the overall weight and footprint of such
systems are of a significant concern in offshore operations.
Designers endeavor to identify ways that the overall weight and
surface area can be reduced without adversely affecting the
efficiency of the system. Furthermore, it is desirable to maintain
a system height that is as low as possible.
[0007] Therefore, there is a need for effective and efficient
systems for offshore processing of high carbon dioxide natural
gas.
SUMMARY OF THE INVENTION
[0008] A first aspect of the present invention is directed to a
heat exchanger used in an offshore low temperature system which
removes carbon dioxide from natural gas. In this aspect of the
invention the heat exchanger is a reboiler in fluid communication
with a fractionator column. The reboiler comprises a rigid vessel
having an outer shell defining a vessel volume. The rigid vessel
has an inlet in fluid communication with the fractionator for
receiving a liquid stream therefrom and an outlet for returning a
vapor to the fractionator. A carbon steel tubing bundle is
horizontally disposed within the vessel volume. Each tube in the
carbon steel tubing bundle has an outer surface and an inner
surface. The outer surface has a porous granular metal layer
deposited thereon. The inner surface is generally smooth relative
to the layer on the outer surface. The granular metal layer
comprises a pore size distribution adapted to promote and increase
a bubble nucleation during vaporization of a nearly pure liquid
carbon dioxide stream.
[0009] This aspect of the invention may include one or more of the
following features, alone or in any reasonable combination. The
granular metal layer may be metallurgically bonded to each tube in
the carbon steel tubing bundle. The shell may be produced from a
carbon steel. A weight of the reboiler may be less than 27,000 kg.
A weight of the reboiler may be less than 22,000 kg. The outer
surface having the granular metal layer deposited thereon may
increase an overall heat transfer coefficient (U-value) of each
tube in the carbon steel tubing bundle at least 1.3 times that of a
bare outer surface of a tube in an otherwise identical carbon steel
tubing bundle. The inner surface may have a plurality of fins
radiating inwardly therefrom. The nearly pure liquid carbon dioxide
stream within the reboiler may have a purity of greater than 90 mol
%. The nearly pure liquid carbon dioxide stream within the reboiler
may have a purity greater than 95 mol %, or about 97 mol %. A
temperature of a bottoms stream entering the reboiler may be
between 10.4.degree. C. and 10.8.degree. C. A bottoms stream inlet
operating pressure may be about 46.5 bar-g. A tube-side stream
temperature within the carbon steel tubing bundle may be between
20.9.degree. C. to 32.5.degree. C. A tube-side stream temperature
within the carbon steel tubing bundle may be between 15.5.degree.
C. to 25.0.degree. C. An outside tube diameter in the carbon steel
tubing bundle may be less than 5.0 cm. An outside tube diameter in
the carbon steel tubing bundle may be less than or equal to 2.5
cm.
[0010] In a second aspect of the invention, a reboiler in fluid
communication with a fractionator column in an offshore low
temperature system removing carbon dioxide from natural gas
comprises a rigid vessel having a carbon steel outer shell defining
a vessel volume. The rigid vessel has an inlet in fluid
communication with the fractionator for receiving a liquid steam
therefrom and an outlet for returning a vapor to the fractionator.
A carbon steel tubing bundle is horizontally disposed within the
vessel volume. Each tube in the carbon steel bundle has an outer
surface and an inner surface. The outer surface has a porous
granular metal layer deposited thereon. The inner surface may be
generally smooth relative to the porous granular metal layer or
have a plurality of fins extending radially inwardly relative
thereto. The granular metal layer comprises a pore size
distribution adapted to promote and increase bubble nucleation
during vaporization of liquid on the outer surface of the tubes. A
liquid carbon dioxide stream is within the rigid vessel. The stream
has a purity greater than 90 mol %. A weight of the reboiler may be
less than 22,000 kg, and the outer surface with the granular metal
layer deposited thereon increases an overall heat transfer
coefficient (U-value) of each tube in the carbon steel tubing
bundle at least 1.3 times a bare outer surface of a tube in an
otherwise identical carbon steel tubing bundle.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] One or more exemplary embodiments of the present invention
will be described below in conjunction with the following drawing
figures, in which:
[0012] FIG. 1 is a representation of an offshore platform;
[0013] FIG. 2 is a simple schematic of a low temperature
distillation process for removing carbon dioxide from natural
gas;
[0014] FIG. 3 is a perspective view of a tube bundle provided in a
reboiler;
[0015] FIG. 4 is schematic of a reboiler used in the process of
FIG. 2;
[0016] FIG. 5 is a schematic of a reboiler used in the process of
FIG. 2 with approximately a 50% reduction in overall size in
accordance with the present invention;
[0017] FIG. 6 is a front view of a tube bundle of the present
invention as provided in a reboiler; and
[0018] FIG. 7 is a front view of a tube bundle of the present
invention as provided in a reboiler; and
[0019] FIG. 8 is a partial perspective view of a tube bundle of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention is generally directed to heat
exchangers used in the separation of carbon dioxide from natural
gas. More specifically, the present invention reduces the weight,
footprint and height of reboilers provided in an offshore system
for removing carbon dioxide from natural gas. A reboiler is in
fluid communication with a fractionator column in an offshore low
temperature system for removing carbon dioxide from natural
gas.
[0021] With these general principles in mind, one or more
embodiments of the present invention will be described with the
understanding that the following description is not intended to be
limiting.
[0022] Referring to FIG. 1, a typical offshore platform 10 for
extracting and processing natural gas is illustrated. The platform
10 is supported above a water line 14 by one or more columns 18.
The columns 18 extend downwardly below the water line 14 to the sea
floor. The platform 10 physically supports a system for extracting
natural gas from below the sea floor. A typical system for
extracting high carbon dioxide natural gas in an offshore facility
may include one or more such platforms 10, each having one or more
subsystems of the overall system. Alternatively, an offshore system
may float above the water line 14. Here, offshore process may be
either a stationary platform 10 as shown or a floating system.
[0023] Referring to FIG. 2, one such subsystem is a fractionator
column 22, or simply a fractionator. The purpose of the
fractionator 22 is to process a gas mixture extracted from below
the sea floor and separate the various components. The components
are then stored, transported, or otherwise disposed.
[0024] One type of fractionator 22 uses refrigeration at low
temperatures ranging from below -20.degree. C. to above 0.degree.
C., more preferably -30.degree. C. to above 10.degree. C. At these
temperatures, the feed gas mixture can be separated by distillation
into a gas stream at the top of fractionators 22 containing mostly
methane and carbon dioxide and a liquid stream at the bottom
containing mostly carbon dioxide and heavier hydrocarbons. In most
cases, the distillation column 22 is operated at a continuous
steady state. A feed 26 is always being added to the column 22 and
a bottoms stream 30 is always being removed. In this case, the
bottoms stream 30 is nearly pure carbon dioxide. Here, the term
"nearly pure" indicates a percentage greater than or equal to 90
mol % carbon dioxide. The bottoms stream 30 may be greater than or
equal to 95 mol % carbon dioxide. A predominantly methane product
32 is withdrawn from the top of the fractionator 22.
[0025] One or more heat exchangers are typically used in
conjunction with low temperature fractionators 22. One such heat
exchanger is a reboiler 34. At least one reboiler 34 is in fluid
communication with the fractionator 22. Feed gas 38, as shown in
FIG. 4, with temperatures significantly higher than that of the
liquid at the bottom of the fractionator, can be used to heat the
liquid in the reboiler 34. The feed gas 38 flows through a
plurality of tubes 42 arranged in a bundle 46 as shown in FIG. 3
and the cooled gas stream 50 is then removed from the bundle 46 and
sent to other heat exchangers or expanders for further cooling
before feeding into the fractionator 22. These reboilers 34 are
generally very large and can have weights that exceed 18.200 kg
(40,000 lbs) and 27,000 kg (59,400 lbs).
[0026] The reboiler 34 receives a liquid stream 30 from the
fractionator 22 and heats the liquid stream 30 by passing it over
the tubes 42 in the bundle 46 as shown in FIG. 3. A liquid product
52 is removed from the reboiler 34 for further processing. A vapor
stream 54 is also removed from the reboiler 34 and returned to the
fractionator 22. The reboiler 34 generally operates under the
parameters set forth in Table 1.
TABLE-US-00001 TABLE 1 Parameter In Out Tube Side Temperature,
.degree. C. 32.5 20.9 Shell Side Operating Pressure, bar 47.5 47.5
Shell Side Temperature .degree. C. 10.4 10.8
[0027] The reboiler 34 includes a rigid vessel 58 having an outer
shell of carbon steel defining a vessel volume 62. The vessel 58 as
an inlet through which a nearly pure stream of liquid carbon
dioxide 30 is received. An outlet is provided to deliver the vapor
stream 54 from the vessel 58. An additional outlet is provided to
deliver the cooled gas stream 50 from the reboiler 34 as shown in
FIG. 4.
[0028] As illustrated in FIG. 3, the tubes 42 are arranged in the
bundle 46. The bundle 46 is horizontally disposed within the vessel
volume 62 as shown in FIGS. 4 and 5. The tubes 42 may be linearly
aligned or form a curvilinear, generally U-shaped, structure as
illustrated.
[0029] As shown, the bundle 46 has an end plate 74 provided with
apertures 78. Each aperture 78 is aligned with an end of a tube 42
wherein the heating gas 38 can be delivered through the tubes 42,
and cooled gas can exit the tubes 42 in a similar manner. The tubes
42 pass through a series of supports 80 which maintain orientation
of the tubes 42 in the bundle 46. In FIG. 3, the bundle 46 utilizes
24 individual U-shaped tubes 42.
[0030] As best shown in FIGS. 4-8, the present invention reduces
the overall size of the reboiler 34 by incorporating a tubing
having an enhanced boiling layer deposited thereon in the bundle
46. This can reduce the number of tubes 42 in a bundle 46. In the
examples illustrated in FIGS. 6-8, the number of tubes 42 has been
reduced by 50% from 24 tubes to 12 tubes.
[0031] The number of tubes 42 can be reduced because such coated
tubing enhances heat transfer efficiency in the nucleate boiling
process. A thin, granular, porous metal layer 82 or matrix is
bonded metallurgically on an outer heat-transfer surface of each
tube 42. Saturated liquid is drawn into the layer 82 by capillary
action and vaporizes from the extremely large number of pores which
exist in the structure.
[0032] In the reboiler 34 of the present invention, increased
boiling heat transfer coefficients can be achieved vs. those of
bare tubes, resulting in an overall heat transfer improvement of
1.3-4 times that of bare tubes. The overall heat transfer
coefficient is generally reported as a U-value.
[0033] In the reboiler 34 of the present invention, the granular
metal layer 82 deposited on the tubes 42 increases the U-value of
each tube 42 to be at least 1.3 times that of a bare outer surface
of a tube in an otherwise identical carbon steel tubing bundle.
[0034] Each tube 42 is produced from a carbon steel. As explained
above, outer surfaces of the tubes 42 have a porous, granular metal
layer 82 deposited thereon. Inner surfaces of the tubes 42 are
generally smooth relative to the layer 82 on the outer surfaces.
The granular metal layer 82 forms pores, which promote bubble
nucleation during vaporization of the stream. The pores also
increase heat transfer area for nucleation during vaporization of
the nearly pure liquid carbon dioxide stream 30. A pore size or a
distribution of pore sizes is chosen to promote and increase bubble
nucleation during boiling on the outer surfaces of the tubes 42. An
outside diameter of each tube 42 is preferably less than 5.0 cm,
more preferably less than or equal to 2.5 cm.
[0035] Referring to FIG. 7, in one embodiment, the inner surface of
each tube 42 has fins 86. The fins 86 extend radially inwardly
relative to the inner surface of the tube 42 and are typically
helically patterned.
[0036] It is contemplated that the use of the tubing 42 described
herein allows reduced number of tubes, smaller vessel size, and
reduced reboiler weight. This is important in offshore systems
where space and allowed overall weight on platform are limited, and
it is desirable to keep weight as low as possible. A comparison of
FIGS. 4 and 5 shows that the reboiler 34 can be reduced in size by
50%. Thus, the weight of the reboiler 34 can be reduced to less
than 9,100 kg (about 20,000 lbs.), more preferably 5,500 kg (about
12,000 lbs.). In one example, the weight was decreased from less
than 27,000 kg, about 26,500 kg (58,300 lbs.), to less than 22,000
kg (48,400 lbs.), about 21,000 kg (46,200 lbs.).
EXAMPLE 1
[0037] Using the principles of the invention discussed herein,
design cases for a CO.sub.2 Fractionator Reboiler having a 2-pass,
U-tube exchanger geometry were generated to provide a comparison of
the benefits of the invention versus a bare tube reboiler design.
The design has been optimized to take advantage of an available
tube-side pressure drop. These design cases reflect calculated
tube-side pressure drop values in the range of 40 kPa-50 kPa (i.e.
5.8 psi-7.3 psi), and the cases are summarized in the following
table:
TABLE-US-00002 TABLE 2 Service CO.sub.2 Fractionator Reboiler Tube
Type Doubly- Enhanced Enhanced Bare Coated Coated Tube Tube Tube
Performance Duty, W 1,943,000 1,943,000 1,943,000 LMTD, .degree. C.
8.4 8.4 8.4 U-Value, W/m.sup.2 .degree. C. 556 803 980 Effective
Area per Shell, m.sup.2 416 288 236 Geometry Tube Material Carbon
Carbon Carbon Steel Steel Steel Exchanger Type BKU BKU BKU
Exchanger Orientation Horizontal Horizontal Horizontal Tube Bundle/
1150/1585 1100/1515 1100/1515 Kettle Diameter, mm No. of Shells 1 1
1 Tubes per Shell 728 870 652 U-tubes U-tubes U-tubes Tube Straight
Length, mm 4877 3658 3353 Tube Diameter, mm 19.05 15.88 19.05 Tube
Pitch, mm 25.4 22.23 25.4 Estimated Exchanger 26,500 21,500 21,000
Weight, kg Estimated Exchanger 1.64 .times. 8.82 1.58 .times. 7.28
1.58 .times. 6.97 Footprint, m .times. m
[0038] According to these results, a suitable option for reducing
size/weight for the CO.sub.2 fractionator reboiler may be a design
utilizing 1.5875 cm OD-coated/ID-bare tubing with an enhanced
boiling layer marketed by UOP, LLC under the trademark High
Flux.TM. or 1.905 cm OD-coated/ID-finned High Flux.TM. tubes as
alternatives.
[0039] Estimated savings in exchanger weight of 5,000 kg-5,500 kg
can be achieved, as well as plot space savings 3.0 m.sup.2-3.5
m.sup.2 associated with smaller footprint of the High Flux.TM.
tubing design options. Both of these benefits carry a higher
premium in this offshore application.
[0040] It should be appreciated and understood by those of ordinary
skill in the art that various other components such as valves,
pumps, filters, coolers, etc. were not shown in the drawings as it
is believed that the specifics of same are well within the
knowledge of those of ordinary skill in the art and a description
of same is not necessary for practicing or understanding the
embodiments of the present invention.
[0041] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should
be appreciated that a vast number of variations exist. It should
also be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention, it being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended claims
and their legal equivalents.
SPECIFIC EMBODIMENTS
[0042] While the following is described in conjunction with
specific embodiments, it will be understood that this description
is intended to illustrate and not limit the scope of the preceding
description and the appended claims.
[0043] A first embodiment of the invention is a reboiler in fluid
communication with a fractionator column in an offshore low
temperature system removing carbon dioxide from natural gas, the
bottom reboiler comprising a rigid vessel having an outer shell
defining a vessel volume, the rigid vessel having an inlet in fluid
communication with a fractionator for receiving a liquid stream
therefrom and an outlet for returning a vapor to the fractionator;
and a carbon steel tubing bundle disposed within the vessel volume
each tube in the carbon steel tubing bundle having an outer surface
and an inner surface, the outer surface having a granular metal
layer deposited thereon, and the inner surface being generally
smooth relative thereto, wherein the granular metal layer comprises
a pore size distribution adapted to promote and increase bubble
nucleation during vaporization of a nearly pure liquid carbon
dioxide stream on the outer surfaces of the tubes. An embodiment of
the invention is one, any or all of prior embodiments in this
paragraph up through the first embodiment in this paragraph wherein
the granular metal layer is metallurgically bonded to each tube in
the carbon steel tubing bundle. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the first embodiment in this paragraph wherein the shell is
produced from a carbon steel. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the first embodiment in this paragraph wherein a weight of the
reboiler is less than 27,000 kg. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the first embodiment in this paragraph wherein a weight of the
reboiler is less than 22,000 kg. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the first embodiment in this paragraph wherein the outer surface
having the granular metal layer deposited thereon increases an
overall heat transfer coefficient of each tube in the carbon steel
tubing bundle by at least 1.3 times that of a bare outer surface of
a tube in an otherwise identical carbon steel tubing bundle. An
embodiment of the invention is one, any or all of prior embodiments
in this paragraph up through the first embodiment in this paragraph
wherein the inner surface has a plurality of fins extending
radially inwardly relative thereto. An embodiment of the invention
is one, any or all of prior embodiments in this paragraph up
through the first embodiment in this paragraph wherein the reboiler
is a bottom reboiler which receives a liquid bottoms stream from a
fractionator column. An embodiment of the invention is one, any or
all of prior embodiments in this paragraph up through the first
embodiment in this paragraph wherein the carbon steel tubing bundle
is horizontally disposed within the vessel volume. An embodiment of
the invention is one, any or all of prior embodiments in this
paragraph up through the first embodiment in this paragraph wherein
the nearly pure liquid carbon dioxide stream within the reboiler
has a purity of greater than 90 mol %. An embodiment of the
invention is one, any or all of prior embodiments in this paragraph
up through the first embodiment in this paragraph wherein the
nearly pure liquid carbon dioxide stream within the reboiler has a
purity greater than 95 mol %. An embodiment of the invention is
one, any or all of prior embodiments in this paragraph up through
the first embodiment in this paragraph wherein the nearly pure
liquid carbon dioxide stream within the reboiler has a purity of
about 97 mol %. An embodiment of the invention is one, any or all
of prior embodiments in this paragraph up through the first
embodiment in this paragraph wherein a temperature of a bottoms
stream entering the reboiler is between 10.4.degree. C. and
10.8.degree. C. An embodiment of the invention is one, any or all
of prior embodiments in this paragraph up through the first
embodiment in this paragraph wherein a bottoms stream inlet
operating pressure is about 46.5 bar-g. The apparatus of claim 1
wherein a tube-side stream temperature within the carbon steel
tubing bundle is between 20.9.degree. C. and 32.5.degree. C. An
embodiment of the invention is one, any or all of prior embodiments
in this paragraph up through the first embodiment in this paragraph
wherein a tube-side stream temperature within the carbon steel
tubing bundle is between 15.5.degree. C. and 25.0.degree. C. An
embodiment of the invention is one, any or all of prior embodiments
in this paragraph up through the first embodiment in this paragraph
wherein an outside tube diameter in the carbon steel tubing bundle
is less than 5.0 cm. An embodiment of the invention is one, any or
all of prior embodiments in this paragraph up through the first
embodiment in this paragraph wherein an outside tube diameter in
the carbon steel tubing bundle is less than or equal to 2.5 cm.
[0044] A reboiler in fluid communication with a fractionator column
in an offshore low temperature system removing carbon dioxide from
natural gas, the reboiler comprising a rigid vessel having a carbon
steel outer shell defining a vessel volume, the rigid vessel having
an inlet in fluid communication with the fractionator for receiving
a liquid stream therefrom and an outlet for returning a vapor to
the fractionator; a carbon steel tubing bundle horizontally
disposed within the vessel volume, each tube in the carbon steel
bundle having an outer surface and an inner surface, the outer
surface having a granular metal layer deposited thereon, and the
inner surface having a plurality of fins extending radially
inwardly relative thereto, wherein the granular metal layer
comprises a pore size distribution adapted to promote and increase
bubble nucleation during vaporization of liquid carbon dioxide on
the outer surfaces of the tubes; a liquid carbon dioxide stream
within the rigid vessel having a purity greater than 90 mol %,
wherein the outer surface having the granular metal layer deposited
thereon increases an overall heat transfer coefficient (U-value) of
each tube in the carbon steel tubing bundle at least 1.3 times that
of a bare outer surface of a tube in an otherwise identical carbon
steel tubing bundle.
[0045] Without further elaboration, it is believed that using the
preceding description that one skilled in the art can utilize the
present invention to its fullest extent and easily ascertain the
essential characteristics of this invention, without departing from
the spirit and scope thereof, to make various changes and
modifications of the invention and to adapt it to various usages
and conditions. The preceding preferred specific embodiments are,
therefore, to be construed as merely illustrative, and not limiting
the remainder of the disclosure in any way whatsoever, and that it
is intended to cover various modifications and equivalent
arrangements included within the scope of the appended claims.
[0046] In the foregoing, all temperatures are set forth in degrees
Celsius and, all parts and percentages are by weight, unless
otherwise indicated.
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